When Eddie Redmayne first met renowned physicist Stephen Hawking five days before the start of the filming of the buzzed-about biopic The Theory Of Everything, he made a "complete fool" of himself in front of the man he would be portraying on the big screen.

"I blubbered and spent the good first half hour telling Stephen Hawking about Stephen Hawking, and he would just smile," the 32-year-old Briton recounted recently to a group of journalists at the Waldorf Astoria in New York City.

Redmayne had done months of research into the 72-year-old English theoretical physicist-cosmologist and his life and Hawking had acquired an "extraordinary status" in the actor's mind.

The research was needed for Redmayne's transformation into Hawking, author of the best-selling 1988 science book A Brief History Of Time. Hawking was diagnosed with Lou Gehrig's Disease at the age of 21 as a University of Cambridge graduate student.

The motor neurone disease is related to amyotrophic lateral sclerosis (ALS), a condition which recently gained mass awareness via the viral activity The Ice Bucket Challenge. It left Hawking a quadriplegic and having to speak through a computer-generated voice amplifier.

In his first leading role for a film, Redmayne - who first captured attention as revolutionary leader Marius in the 2012 movie musical Les Miserables - had to portray Hawking's 25-year evolution from being fully functional to having use of only a few muscles, eventually limited to facial movements, his voice superseded by a machine.

To prepare for such a daunting part, Redmayne visited an ALS clinic every couple of weeks for months, worked with an ALS specialist, a vocal coach and a movement director.

He also spent months working on facial contortions, so much so that he could show them effortlessly in front of us during the interview.

"With ALS, once the muscles stop working, you use whatever you can. So all these muscles I never use, I just spent months in front of the mirror with documentary footage trying to replicate those aspects, but also trying, more than anything, to capture the mischief, this glint in his eye, this humour and the capacity to control a room even though he says very little," he said.

Redmayne, who admitted the pressure of playing such an iconic figure had given him "a year of sleepless nights", said the physicality was only part of the challenge.

He also had to nail the emotional dynamics between Hawking and his first wife Jane (Felicity Jones), who started a family with him despite his diagnosis, and the journey they took to defy the disease together.

"I had to embed all of the physical work so that when it came to Felicity and I, we had to just be there and play the human story," he said.

"So that was part of the process of those rehearsals - getting your muscles used to these things so that you can sustain for longer periods of time."

The Theory Of Everything director James Marsh said Redmayne was the first actor he met for the film and he was convinced his leading man, who had theatre experience and won awards for his stage performances in Red and Richard II, had the fortitude and talent to pull it off.

"He knew what it was going to take - months and months of difficult physical and psychological preparation," said Marsh, who won an Oscar in 2008 for his documentary feature Man On Wire.

And the efforts have paid off, earning Redmayne rave reviews and Oscar buzz since the film premiered at the Toronto International Film Festival in September.

Alongside Benedict Cumberbatch and Tom Hiddleston, he makes up the latest crop of British heart-throbs who are increasingly making a splash in Hollywood and gaining legions of rabid female fans.

The Theory Of Everything has also earned approval from Hawking himself, who travelled to London for a screening from his home in Cambridge, and according to a Variety report, had his nurse wipe a tear from his eye after the show.

REWARD

"What was lovely was after he saw the film, he gave us his voice," said Redmayne, referring to Hawking allowing the filmmakers to swap the synthetic voice they had been forced to create and replace it with his own trademarked computerised version.

"For an actor, that's a tiny little step closer to reality, so that was really wonderful."

Redmayne deftly sidestepped a question about his Oscar chances, calling the Hawking family's "incredibly generous" response to the film as the "greatest of rewards".

"The story, given how specific the circumstances are, is pretty universal, about being given obstacles in life, and how you choose to supersede them. And the buzz and - don't get me wrong, it is incredibly flattering - I hope it encourages people to go see it."